[Lazarus] Linux: howto define file *.lpi to be opened with lazarus?

[John Landmesser]

I'm on Linux-Mint Cinnamon and i want to associate *.lpi with lazarus 
Application:

*.lpi is of Filetype XML, but we need the fileExtension *.lpi here!!

found:

lazarus.desktop

copied:

  cp '/home/john1/lazarus/install/lazarus.desktop' /usr/share/applications/

and

lazarus-mime.xml

copied:

  cp '/home/john1/lazarus/install/lazarus-mime.xml' 
'/usr/share/mime/application/'

Content of these two files seems to define for what i'm looking for, but 
reboot wasn't enough.

What i'm missing to get the filetypes/extension-Database updated?

Tipps are welcome!!